The Seas They Are A Changin’: Regular monitoring reveals biological changes in Maltese waters

The Mediterranean Sea is a sea of change. Its temperature, salinity and circulation patterns are primarily determined by the prevailing climate, which renders this sea highly susceptible to climatic fluctuations, both long and short term ones. Climate models indicate that the Mediterranean region is one of the hotspots of global climate change, and the Mediterranean Sea is already responding to these changes, as evidenced by an ongoing warming trend in both the surface and deep waters of this sea. Such environmental changes can have significant effects on Mediterranean marine biodiversity, such as enabling the entry and spread of non-indigenous species or leading to changes in the distribution and abundance of native species, but this can only be ascertained through regular biological surveys.

The Maltese Islands are ideally placed to monitor biotic changes in the central Mediterranean, particularly given their location within the Sicilian Channel, which serves as the chief passageway for species to extend their range from west to east or vice versa. Taking advantage of this fact, the Marine Ecology Research Group (MERG) at the Department of Biology of the University of Malta has been undertaking regular biological surveys to monitor changes in the status of marine species and habitats in Maltese waters. For instance, since 2008 this research group has been actively participating in the ‘Tropical Signals’ programme, which was launched by the Mediterranean Science Commission (CIESM) with the aim of detecting, monitoring and understanding the effects of climate warming on Mediterranean marine biodiversity. In addition, MERG researchers also collaborate with local entities, such as the Malta Environment and Planning Authority, who are also concerned with monitoring local marine biodiversity.

Although long-term monitoring is needed to allow meaningful analysis, the regular surveys undertaken by MERG and its collaborators have already led to several notable findings. For instance, recently, two new alien seaweed species have been observed in Maltese waters. The first, the red alga Acrothamnion preissii, was observed in Cirkewwa and Dwejra in April 2014 during ‘Tropical Signals’ surveys, while the second, a variant of the green alga Caulerpa taxifolia, was initially observed at Baħar iċ-Ċagħaq in June 2013 during surveys organised by MEPA’s as part of its participation in the MedPAN North Project, and was subsequently confirmed to have established populations at another two sites by the University researchers. Besides new introductions, the surveys have also revealed changes in the abundance of certain species. In particular, the alien rabbitfish Siganus luridus, which has been present in Maltese waters at least since 2002, but which was initially only sporadically sighted, now appears to have become well established with an increasing number of records in recent years. Similarly, the native alga Sargassum sp. seems to have become more abundant at certain sites, with a marked increase in frequency recorded in 2014 compared to previous years. Both these species are considered to have a warm-water affinity, that is they thrive in warmer waters, so their increasing abundance is likely linked to the warming trend of the central Mediterranean waters.

Although these findings are only preliminary they do portend further biological changes in Maltese waters, but such changes can only be detected through regular surveys, highlighting the need for ongoing monitoring of the local marine environment.

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The Marine Ecology Research Group welcomes reports of any unusual or new marine organisms. Please contact the Group Leader, Prof. Patrick J. Schembri, at the Department of Biology, University of Malta on +356 2340 2272 or by email.

(a) Fronds of Caulerpa taxifolia var disticophylla, first recorded from Malta in June 2013 [Image by Sandro Lanfranco]; (b) photomicrograph of Acrothamnion preissii, first recorded from Malta in April 2014 [Image by Veronica Farrugia Drakard]; (c) fronds of Sargassum sp., a native alga that seems to be increasing in abundance [Image by Julian Evans]; (d) the Dusky Spinefoot, Siganus luridus, an alien fish that also appears to have become more common [Image by Reno Micallef].